import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long x = in.nextLong();
        long[] nums = new long[n + 1];
        int k = n;
        while (x > 0) {
            nums[k--] = (int) (x % 10);
            x /= 10;
        }

        int count = 0;
        for (int i = 1; i <= n; i += 2) {
            if (nums[i] != nums[i + 1]) {
                count++;
            }
        }

        System.out.println(count);

    }
}
